The objective of the proposed research is to determine the molecular mechanism of intracellular transport. Organelle movement will be studied in isolated chromatophores and leukocytes. The function of actin, tubulin, and microtubule-associated proteins in intracellular motility will be investigated in four ways: (1) Cells will be fixed while under observation in the light microscope and stained with fluorescent-labeled antibody against tubulin and actin to determine if organelle movement is associated with microtubules or actin filaments. (2) The inhibition of movement will be examined in chromatophores and leukocytes and in actin-based systems of motility using myosin subfragment-1 and antibodies to tubulin and actin. Since these ligands bind to tubules and actin filaments specifically and with high affinity, it may be possible to block their function in the cell and thereby determine their requirement for motility. (3) Microtubule-associated proteins from brain tissue will be examined for enzymatic (ATPase) activity and for their ability to to crosslink microtubles to each other or bind microtubules to other filaments and membranes. These studies will be used to determine if the brain microtubule-accessory proteins perform a crossbridge function that is required for motility. (4) The properties of brain microtubule-accessory proteins will be compared with those of microtubule cross-bridges isolated from the marginal band of avian erythrocytes. These studies will be useful for explaining the observed microtubule-dependence of intracellular transport and for determining the mechanism of intracellular motility.